Honestly -- the 8 ft long foam (Resiflex) 'on-the-floor' beam is really all you need if you must buy one. They are fairly inexpensive, easy to store, and safe.
Or, even easier -- A double wide line on the floor with 2" duct tape. It really is all you need. A 4" wide straight line that doesn't grab your bare foot when you move. You can even make this full regulation length (16') if you have the space.
For your mom:
I build my dd's beam because I do woodworking as a hobby, and wanted the home beam to be exactly like the gym beam in width, taper, and beam cover. I've seen many a home beam that isn't regulation width, covered with thick carpet (scary), or isn't covered at all and has a very slick wood finish on it. (even scarier still).
From my perspective, If it's not at least close to what's being used at the gym, it's usefulness is very limited and could infact have negative results. You end up having to "unlearn" what you taught yourself at home. Keep this in mind when choosing.
Our low beam is 10' long (laminated spruce), 18" high 4" wide with 1/8" punched felt under a waxed swede beam cover.
What I've learned:
A short elevated beam doesn't provide much advantage over a piece of tape on the floor. That little height / length is fine for practicing handstand, a little acro, and some dismounts - but not routines. Just single elements.
Also - Upholstry swede is too grippy by itself. A light weight wax helps with this without making the beam slippery. It should be soft but stiff enough to support weight, and it shouldn't grab the foot when doing turns or pirouettes. Most consumer beams in swede aren't anything more then low-grade upholstry swede. It's not a "beam cover" as you may think of one. A true beam cover is a very specific grade and composition.
This is also why carpet covered beams should be avoided. You'll end up over-compensating skills, which is counter-productive to your training.
