Joint laxity in the female persuasion is quite common (at least more common than in men). Also, about every 28 days, it will increase due to hormonal changes.
Any chance her period got screwed up during training? This is quite common too. Intense training and lower body fat has a way of altering timing of hormonal cycles.
You can't rehab away joint laxity, it's genetic, but you sure as hell can rehab the injuries once the acute stage begins to subside. She can also get stronger and "learn" to improve stabilization through proper training.
Pet peeve warning...if the doc actually said strained ligaments, please kick him (or her) in the gonads with my compliments. Ligaments are sprained, muscles and tendons are strained. I feel much better now.
I'd get her checked by an orthopod ASAP just in case because she's an athlete and intends to return to sport. If there was any torque on the knee when the ankle gave way there could be more joint related injury beyond a sprain.
So your wife is chick boxer....
Hmmm...Hey David, I've never seen your wife naked but I've seen her box! (couldn't resist

).
Women boxers...what's next...women voters!!
Let me know how it goes and if I can offer further commentary.
Bill