Yea forget the steroids. It takes time to start a major change in your physique and its going to happen at the rate your body can do it. 6 months aint' nuttin if she's looking for significant muscle growth or fat loss. In fact, what exactly is her goal right now? I"m not totally clear. Also how tall is she?. Also at 25% bodyfat (mind you this is not "fat" for a typical female), she still has plenty of ways to go both in muscle development and fat loss. If you throw in steroids now she's going to end up "thick". Steroids aren't fat burners and they don't perform miracles - but you start running a cycle expecting to lean out, starting at more than say 13-14% bodyfat, you're going to end up thick. Additionally if she dives in immediately w/o giving her body time to respond to the training & diet, as mentioned above -she's going to have a hard time understanding how her body responds to diet/nutrition, training and cardio. ****ing w/ your hormones adds a whole other level of things your body has to deal w/ as well as your expectations and ability to properly view where a cycle fits in the overall plan.
I get she's seeing results on you - but how long have you been training? Years I bet. What does your diet look like? Clean and consistent I bet How consistent are you? Very consistent I bet. Oh yea, and you have a completely different hormone profile than she does. All of these are HYUGE differences and popping steroids are not the common point. What you do won't translate to her world. So the expectations need to be kept in line.
As RR said - can you post the diet & training in detail? These are the foundation and MUST be consistent, well-established and producing the results you want before you should ever even consider a cycle. I would very much tell your gf to not worry about the steroids and spend a lot of time focusing on well-established diet, getting her form in place and tight and establishing the discipline of a good bodybuilding lifestyle. If she has good muscle building genes, then you will see the results w/ diet & training. Don't say that to justify the drugs.
I"m also curious on what you base this t3 cycle? 25 mcg EOD?
Has she ever had any hormone panels done? Does she know her body's natural state of thyroid hormone production? Estro? Progest? Test? Lipids? Cholesterol? I'm asking this because, particularly in women, even something as simple as diet change can produce change in hormone production. (And again, another point backing up why extrapolating steroid use by males, to women - it just doesn't work the same so its critical that women don't use the "It works for him" reasoning to dive into steroid use.)