If you can remove both doors, bring them with you to a Kitchen & Bath Retailer. You can call a local Plumbing Supply House (found in the Yellow Pages under PLUMBING - SUPPLIES), and ask them if they know of a place that EXCLUSIVELY sells Bathroom 'stuff' (in the least.) (In my area, there's a Kitchen & Bath store right next to a Plumbing Supply House. How convenient!)
If you can only remove 1 door, do measure the WIDTH of the stationary door. (Its HEIGHT is the same as the door you removed.) Then, measure the entire 'opening' that the casing sits in. Take the door(s) and the measurements to the Store. You may luck out but then again, ask about your 'options' if there isn't an exact 'fit'. (They may be able to 'shorten' them or something, and re-use them if your Mom permits it.)
Other than that, maybe someone else has something to offer. My best to ya and hope this helps.
PS: After this afternoon, I won't be back until Tuesday morning but others will be 'around' ...