Commenting on my weight loss very rudely!!help!?

there is this lady who is 36 yrs old with a 7 yr old son.iam 27 married for 3 yrs not kids yet.i work so hard to maintain my fluctuating figure(i have the tendency to put on weight easily).so some friends complement me for maintaining.this lady never ever appreciates me but whenever i put on a little bit of weight she is lik"oh! r u pregnant..ur looking plump..now only u look normal!"..etc etc.it hurts me and iam not thekind to retort.i stopped talking to her.tommorrow i gotta party for a dear friend and i gottu be there!that lady is also coming.i heard she even lost a lot of weight than me .well..now she woul be even more bitchy.what do i do?i cannot avoid the party.