it could be ascites , (fluid >sometimes referred to as "waterbelly" but also sometimes described as you just have) or it may indeed be eggbinding in which case you can give her a crushed tum (this is an emergency substitute for the calcium gluconate a vet would also give) and place in a warm bath for 10-15 minutes and on a toasty warm towel after and dry her to prevent chilling and give her POLYVISOL to address any d3 deficiency (three drops a day for a week then taper off the next)
Kygel to "lube "' the area will also sometimes help.