Being 'in bloom' means that a rose (or any flower) is at it's most beautiful stage, petals all opened out, turned upward towards the sky etc. It's when a flower looks at its best. Then it starts to fade, the petals curl and so on - and the rose begins to lose its appeal, as the bloom has passed, it is 'off' the rose. Figuratively, as in this expression, it can mean that the initial feeling of encountering something new and exiting is beginning to fade. In this example the couple arrive in the town optimistic and maybe like the look of the place - their experience of the town is 'in bloom'. Then they hear about raining toads, and the bloom fades (pretty quickly I should think). 'This mother's daughter' is just a way of saying 'this woman', i.e. every woman is the daughter of a woman.