***DISCLAIMER: I AM NOT SAYING SUICIDE IS WHAT HAPPENED HERE***
That being said, it's actually extremely common for people with bipolar disorder to commit suicide when they are manic or hypomanic. Mania includes impulsivity, a lack of future thought, grandiose ideas, etc. It's also not always euphoria; it can also present as extreme anger. Additionally, someone with bipolar knows what it is like to feel both the highs and the lows, so when someone is manic and seems like everything is going great in their life, they also know what will be coming after: an incredibly crushing low. Some people make an impulsive decision to avoid that crushing low while they are in the throes of a manic episode.
Source: Someone with bipolar disorder II who also knows multiple people who have done or planned to do the above.
If this were the case, she likely would have turned up by now. JMO.