My gf is insecure about her body and I don’t know what to do

I’ve been dating my gf for about a year now, I’m very much happy with her and genuinely do love her very much not just because she’s my first girlfriend but because I genuinely feel like she gets me as a person. I’ve known my gf has had some insecurities about herself like her height since shes 6’2 if i remember correctly, her weight because she’s really skinny and struggles to put on weight and her flat chest but shes always seemed somewhat content with it so i never really thought much about it.

Around 2 nights ago while we were watching movies late at night at my house she asked to pause the movie so she can ask me a question obviously I said sure and she proceeded to ask me if I’m confutable with her body. I was caught off guard and I found it odd that she asked me it since we’ve never had sex nor have I ever said anything bad about her body. I said yea I don’t really have a problem with her body but then she immediately started crying proceeded to say that she doesn’t really believe me I tried comforting her the best I could and tried to reassure her I think she’s pretty.

After a while she finished crying and then told that that recently her insecurities have been getting worse and worse and how her body makes her feel out of place in most places. She saids she strugglesbuying bras that fit because of her flat chest and wishes she had a bigger chest size, how she sometimes feels too tall for a lot clothing and places and how she dislikes going to places like beaches and lakes since of how skinny she is. She also told me that she wants to believe me when I say I don’t have a problem with her body but can’t not because she doesn’t trust me but because she feels like I’m only telling her what she wants to hear because I’m her bf.

after she felt somewhat better I drove her home we haven’t really talked much about it but I feel bad like if I could’ve told/did something that reassures her and make her believes me. I don’t want her to feel like I’m just telling her stuff she wants to hear just because I’m her boyfriend but I just don’t know what to say or do.

Thanks in advance if someone gives me advice also sorry I wrote so much didn’t expect to write a lot

(TLDR: My gf is very insecure about her body and I don’t really know what to do)