All but one of the women in our group dive in drysuits. I would recommend getting a drysuit for her and then getting her some training. The general rule of thumb is that people who are not comfortable while diving will dive less or stop. She may say she gets cold around 15 minutes, but my guess is she is colder sooner than that and just doesn't want to spoil your dive.
I have dove both wetsuits and drysuits along the California coast and I highly recommend drysuits to anyone who wishes to dive here often. Also, don't settle for a really low cost suit or a semi drysuit. Spend the money and get a good one, it will last you twenty or more years if you take care of it. There are reasons for a drysuit to leak or be uncomfortable, but all can be prevented with proper care and sizing. The key is training and yes it does take a few dives to get comfortable with them.
I have dove both wetsuits and drysuits along the California coast and I highly recommend drysuits to anyone who wishes to dive here often. Also, don't settle for a really low cost suit or a semi drysuit. Spend the money and get a good one, it will last you twenty or more years if you take care of it. There are reasons for a drysuit to leak or be uncomfortable, but all can be prevented with proper care and sizing. The key is training and yes it does take a few dives to get comfortable with them.