Currently (August 2016) the tips notes say that beidio is "to refrain from". I think it should be mentioned that the basic form of "to refrain from" is peidio which has undergone soft mutation because of the rhaid construction. Otherwise it just causes confusion because the examples use beidio, but it is also stated explicitly that verbs after rhaid should undergo soft mutation, so one might think it should in fact be feidio.
Just a bit of advice. We don't really use the word lenition in Welsh instead we say "soft mutation.
Because â is the version that comes before a consonant and ag is the version that comes before vowels.
why is the correct answer "Morgan must not wash herself" rather than "... wash himself"? I would think Morgan is a man's name.