I think instead of chastising her for doing DIY, we should offer some support. Some people do what they have to do in order to be themselves. Sometimes, it's via methods we don't always agree with but it isn't something to be judged and chastised over.
Estrogen has not been shown to be an addictive substance (if it was, trans men wouldn't exist). However, when people on HRT don't take the meds for a little while, their hormone levels will trough and once you are back on, you feel relieved. This is a perfectly natural feeling when one is one hormones and the levels drop and rise. Estrogen is also responsible for production of serotonin which is the "happy hormone" that helps make you feel good. When post-op women halve their dose of E do to having gotten surgery, it is more likely that post-op depression will occur because your level of serotonin will drop as well. This is why post-op trans women should not halve their dose of E until at least 6 months after surgery. The same thing happens when you stop taking hormones for a little while, you fall into a trough then when you're back on, you feel the rise. There is also a psychological aspect too, the feeling of being more calm because you know you are back on E.