I strongly suspect my younger sister has been stealing from me and my family. Am I overreacting?

I strongly suspect my younger sister has been stealing from me and my family. Am I overreacting?

I have two sisters. My younger sister has a long history of lying and distancing herself from the family. She rarely talks to any of us anymore, but then complains that nobody talks to her, even though she was the one who stopped communicating first.

We all live in different countries from the rest of our family. My younger sister lives about two hours away from me and visits occasionally.

Earlier this year, $300 CAD went missing from our condo. We had $500 CAD in a pouch that my older sibling had given me as a gift. My younger sister knew about the money because she saw us put it in a drawer. The day all my siblings were visiting was also the day everyone was leaving. After everyone left, I checked the pouch and $300 was missing. Nobody else had been in our condo, and we don't have outside visitors.

At the time, I didn't want to accuse anyone, so I let it go.

This past weekend, my father-in-law came from our home country to visit us. He had about $1,300 in his wallet because he wanted to give us some money as a gift. The day before, we went on a short trip where he took his wallet out, so my sister saw that he had cash.

The next day, after he counted the money and put it back in his wallet, we discovered that the cash was gone within about an hour. We also checked my wife's wallet, and another $300 was missing from there.

Again, there were only four of us in the house—my wife, my father-in-law, my sister, and me. There were no visitors, and nothing like this has ever happened except when my sister has been around.

After this happened, I searched through old messages with my girlfriend (now my wife). I found a conversation from about five years ago where I had told her that money had gone missing from my car after my sister had borrowed it. My wife had asked who had taken the car, and I replied that it was my sister. Seeing that old conversation reminded me that missing money wasn't a one-time incident. There have been other occasions over the years where cash disappeared, but I was always told I was just careless.

My wife was actually the last person who believed my sister could do something like this. She always defended her and thought people judged her too harshly. But after witnessing these recent incidents herself, she now also believes my sister is the most likely person responsible.

There have been other things that make me uneasy as well. Last week she lied and said she couldn't visit us because a friend was visiting her, but we later found out she had actually flown somewhere else and didn't tell anyone. On another occasion while we were camping, she quietly took a barbecue grill from a grocery store. Nobody confronted her because we weren't completely sure what had happened.

After the money disappeared this weekend, I told her that we had searched the entire house, including clothes, luggage, the washing machine, and even the garbage. I also told her I was considering filing a police report for insurance purposes. She calmly replied, "Yeah, okay. Let me know how it goes."

About an hour before she left, she suggested that I check near my father-in-law's suitcase. I couldn't check immediately, but when I did later, there was nothing there. Throughout the whole situation, she remained very calm and confident, as if nothing had happened.

I know none of this is proof, and I don't want to falsely accuse anyone. But after multiple incidents over several years, all occurring when she was present, I'm finding it hard to believe these are all coincidences.