Could it be a health issue? As this has started a week back only.
No-one (that I know of) decides to wake up one day and say "hey, I'm going to just start belching every few minutes for the fun of it!" Sounds very much like a health issue to me, and probably one that she's aware of and potentially embarrassed by.
If you must say anything to her, then be nice about it and ask if she's doing ok. If your issue is just the noise though, I'd try to take steps that don't involve bringing her into it, eg:
- Wear noise cancelling headphones if you have any, and listen to music
- Ask if you can work elsewhere, perhaps at another desk in the meantime
If these aren't feasible, then just take the issue to your manager and let her deal with it - part of her job is to make sure you have an effective working environment, so she can then address the situation as she sees fit.