In my experience, Blue Cross tends to be the most expensive, but they are also the best (everyone takes them, they're fairly honest, etc.). Stay away from United Health Care!!!! They forced me to pay my $2000 premium twice in one year, I had doctors' bills which should have been paid by the insurance company, since I had already paid my deductible. However, UHC kept insisting that they didn't receive any payment information from my doctor (which isn't true -- my doctor sent it three times), and my credit was going to be ruined if I refused to pay the bills for which UHC was actually responsible. I spent a year wrangling with them, but, in the end, I ended up paying the extra $2000. From what I've heard, this is a pretty common practice of theirs.
Also, no matter which company she chooses, she needs to be aware that insurance companies in Texas DO NOT OFFER MATERNITY COVERAGE FOR INDIVIDUAL PLANS!!!! I found this out when I had Blue Cross. I asked the BC rep, "So you're telling me that anyone who carries individual insurance doesn't have maternity coverage?!?!" and she just said "Yep." According to my broker, Texas doesn't require insurance companies to offer maternity, and, since it's very expensive (for the company) and it usually gets used regularly, companies don't offer it. The only way to get coverage is to buy special maternity insurance (which can be more expensive than paying out-of-pocket), or try to get into a group plan (offered by employers of larger companies). Although she may not be thinking about babies right now, you never know what the future holds, and, considering that my son's c-section cost over $20,000, I'd be careful not to take the risk.