Yes, angioplasty is about dealing with problems in blood vessels wherever they occur in the body, which includes the major vessels in the leg.
Bypass surgery is about using methods to bypass a problem area, which again can occur in various places in the body, not just related to the heart.
Bypass surgery in the leg usually means taking a peripheral leg vein and using that to bypass the affected vessel.
As far as the risks are concerned, either procedure has some risk but does have a good outcome. For a short while I worked for a vascular surgeon in a district general hospital. Angioplasties were carried out by the radiologists, but only when the vascular surgeon was available in the hospital in case they needed to call him in, and that was a standard protocol.
For the bypass surgery, a peripheral vein (the long saphenous vein) is harvested and connected to the top and bottom ends of the affected artery which is then disconnected, so allowing blood to flow from the groin to the lower leg. The blood flows back up via deeper veins as usual.
From what I can recall, there were two major areas of risk. One is if the peripheral vein in the same leg wasn't viable, which would mean the peripheral vein of the other leg would be needed. The risk there is if problems subsequently developed in the other leg, where of course that peripheral vein would no longer be available. But blood vessels in reality aren't exactly what is illustrated in medical text books, to the extent that quite probably no two legs are the same even in one individual.
The other risk would be as in any other surgery, which would be to do with general health, reaction to anaesthetics, any other mobility problems, etc.
Obviously I'm not an expert (I just worked for one for a while), but both angioplasties and bypass surgeries were carried out on a weekly basis in the medium-sized general hospital I worked in.
There is more information via the link I posted, but I know that medical terminology can be a problem for people who don't get to hear it every working day. Bypass means just that, heart/roads/whatever, but the usual name for the kind of bypass surgery you are thinking about is called femoropopliteal bypass surgery and if you click through on that link you'll see an explanation as to that type of bypass surgery.
Hopefully, an angioplasty will be all that your mother needs. But if she subsequently needs to go on to bypass surgery she'd be one of thousands per year who benefit.