For better or worse 11/12 is the age such feelings start to develop and the appropriate way to respond is to put it bluntly "Not care". The reason for this is twofold.
1: It doesn't matter if she likes girls or boys as long as she is happy, right? Then don't make a big deal about it. By letting her find out herself what she likes she won't feel pressured. Sure you might just want to support her, but if you are over supportive of the possibility that she might be lesbian (or bi), she might feel pressured to also think it because it might make you happy. And the same might happen if you are more supportive of her being interested in boys. Best is to be an observer in the development rather than an active participant so she can truly make her own decision. In the meanwhile just show her that you love her for who she is not for what she likes.
2: She is just a kid, and it might be just a phase she is going through. It might be more curiosity than anything else. When I was around 15, I had 4 lesbian friends who were a year or two younger than me. Now one of them is bi, two are fully straight and one is happily married to a girl. Again the important thing is to let her discover it for herself and just be a loving parent :) The whole "it's just a phase" thing might sound cliche, but in some cases it's just true, but it's up to them to figure it out.
Because if you let her know she is loved, and if you let her follow her own path, she will come to you when she needs it. And let's face it, no teen wants their parents butting into their love life, and trying to can have counter productive effects of them trying to keep it more secret. My mother for example was so overbearing that I had a relationship for about 8/9 months and she knew nothing about it due to her being overly involved...while my dad knew it in the first two months because he was more casual about it.
And I get that you are afraid she might be getting confused because of the internet and I can't really blame you for it. About 2 years ago my neighbor's cousin (13) went topless live on Facebook to declare she was a boy and wanted to be treated as such... turned out she was just a girl who had it rough (neglecting parents) who wanted to feel special and luckily got the help she needed. I'm mentioning this because (in my opinion) the media glorifies being LGBT+ a bit too much, in which young impressionable teens feel like it would make them special if they also were like that and get more love/attention. (From my previous example the two girls who turned out to be straight afterwards both came from households where the parents weren't in one way or another available for their children.)
The bigger problem here is the internet connection. I have a lot of friends I met online (my best friend for more than half my life for example), and personally I have never run into any trouble, but I have also met people who did. Sadly a lot of people pretend to be younger and catfish young girls.
Ways to prevent such problems is to check if they are real. which can be done using a few tricks.
Google reverse image search allows you to upload a picture and check if there are any other sites that contain it. This is an easy way to check if the person is using pictures that are not his/her own.
Social Media because most people who meet others online have social media accounts like Facebook/Instagram. Things that add to their credibility. If there is only 1 or two pictures it becomes a bit of a red flag but if the person in question has a lot of visible connection (like the girl's mother commenting on her picture, or her being tagged in a family photo posted by somebody else or in a post of a friend she went shopping with or something like that). If the account has no family members in their friends list and only young girls it's another red flag.
Videos/sound are also good boost towards their credibility seeing they are harder to fake, so having them video chat or a phone call would be a good indicator...but if the person in question is only able to provide pictures and nothing else it becomes alarming.
None of these options are 100% fail proof but will help a lot with identifying possible threats.
Meeting in person is also a good option seeing it removes any doubts but with this it's a matter of being extra careful. Keep it public, and at best under parental supervision. When I was 16 I knew a girl online and we decided to meet up. She chose the place (public restaurant) and took a friend along while my parents dropped me off there and stayed until I texted them it was all fine. But with this it's of course always good to stay close and public for the first few times.