I would go ahead and start her on the water now and I would also go ahead and put a call into her doctor too. (They are on call after hours) he may want to call in something for her to help her faster. It may take 24-36 hours or so by the diet change. Plus with you saying she's not comfortable, and with this being caused by the medication, she may need a little help with medication to get some pressure off.
Hope this helps..