You should also try the referral services of ISSA and NASC, NASM and IFPA:
www.nsca-lift.org/trainers/
www.issaonline.com
http://www.ifpa-fitness.com/Locator_...alTrainer.aspx
In my opinion, the certifying organization matters far less than the experience of the trainer. Each organization has a slightly different set of "blinders" through which they view fitness: ACE is very academic, but the actual course teaches very little about training. ACSM certification was developed from a medical standpoint and is the oldest certification around, but has very little practical "trainer-training". ISSA is geared towards bodybuilders and powerlifters. NSCA is mainly concerned with athletic conditioning although they have added a new Personal Trainer certification. IFPA claims they are the only organization training "fitness professionals" who look at the whole picture.
Trainers collect all sorts of certifications for various reasons. Certifications are good for 2 years, then have to be renewed by either taking continuing education credits and submitting them to the original certifying organization, or by just testing for a new certification from another organization. That is usually also accepted by the first as a continuing ed fulfillment, and then both certifications are in effect. It's usually a lot cheaper to test again than to take continuing ed courses, so if someone has been training for a while, it's not unusual to have or have had 3 or 4 different certifications.
If I were looking for a trainer, I would start asking around for recommendations rather than worrying about the particular certification. Anyone who is certified by any of the above organizations has the knowledge, but as you've discovered, they may not have the experience or enough experience with someone with your particular needs or concerns. Do you know anyone your age who has used a trainer that they could recommend?
Ask around your club if you don't personally know anyone. Try approaching other women who seem comfortable in the gym and ask them if they've worked with a trainer and who they would recommend.
Mel