How to get my almost 4mo. old to take a bottle.?

We had a hard time with feedings in the beginning, so after we finally got the feeding thing down, I didn't want to give her a bottle. Now after only feeding for about 2 months, she wont take a bottle. She doesn't even try to suck, she just cries and gags a little. What can I do? I've tried different bottles, and , I bought a advent sippy, I just don't know what to do at this point. Please someone help me!!