Latty, I really don't know the answer to that. If it were me, I'd have a vet out to check her, not so much because I think her being gassy is a problem, but to make sure everything is alright. You need to establish a relationship with the vet, so he knows your mare, etc. just in case you need him when the foal arrives. He/she can answer all your questions.
Thanks for reading my article. I hope it was helpful.