Do you have any IRL friends that know and are supportive? Having some backup physically with you when you come out can really help with nerves … it’s a really difficult thing to do, so how you’re feeling is natural.
Your mother’s reaction sounds like either a kneejerk reaction, it’s very easy to be pro-LGBT when you’re not directly confronted with it … with a shock like that some people fall back on the homophobia they were raised in (that stuff sticks like dog doo to the bottom of your shoe). Take care of yourself first and foremost, but try and be patient with her - given time and space she might come around on her own or with just gentle nudging.
Whatever happens, in the world (both online and IRL) there are people who will genuinely support you and love you for who you are. Being brave enough to step out into the light is the hard part, and you’ve already taken the first step towards that - you can do it!