There are 3 broad categories of users. Ladies who feel they missed their boobie installation during puberty. Ladies who due to weight, illness, breastfeeding and/or age have lost volume or perk/firmness and wish to regain it. And a male user base who desire feminine breasts for various reasons.
So, she is a good candidate. As I've has seen, age isn't a show stopper (it does have a factor in speed but it doesn't prevent). There is a 77 year old male who is my hero with noogling. She can do this if she really wants the benefits.
As for time... who knows... Each person is quite different in effort and response. If she truly only seeks a firm-up then 6 months is a reasonable first guess at a time frame. But I'll warn you... once you get a taste of that swelling and potentials; it can be quite hard to not want more (even with her 38DD).
Any way you view this activity, it is a long term project and I like to think a fun one. Feel free to read the forum and focus on the STATS and GALLERY sections for real examples (both success and failures).
DJ