How quick can someone with bipolar go from a manic phase to depression?

Is it possible for someone with bipolar, during the very same day, to go from very happy to a sudden depression that last for weeks?

Here's the back story for those interested. It happened few years ago but I still feel the need to get answers because this was an emotional trauma for me. I'll try to keep it short with a timeline:

May 2016
A female coworker (we're both married) who is very reserved, out of nowhere makes the first step to start friendship with me. We play pool in the office, she shares her cooking with me. Lots of positive energy!

June 7th
After playing pool in office like everyday we keep the conversation online during working hours.

June 8th
We chat online the ENTIRE day during working hours! She invites me to go to a surprise "beautiful place" during lunch hour (it was simply an Indian supermarket). It's a long walk, we talk, laugh and get lost on the way so we never made it to the shop. That night she waits for me to finish work so that we leave together and talk some more.

June 9th
When I arrive to the office she surprised me with a very elaborate dish she cooked the night before. Within half an hour of eating my dish she says she wants us to go to supermarket next door so we go, she's so happy. She tells me stories and laughs to tears. We keep chatting online the ENTIRE day and we finally went to the "beautiful place" during lunch hour. That night she waits for me to finish work so that we leave together again. At that point I feel like we're the best friends in the world, nothing can take us apart.

June 10th
As soon as she arrived in the office she was so excited that barely had time to sit on her chair than she messaged me to write on a piece of paper so she can analyze my writing. She says that she has a gift for me and asks if I want it now or during lunch time. I say lunch time and we keep chatting online. Now just before lunch time she goes for a work meeting. She comes back shortly to her desk and she messaged me "I need to talk to you". She leaves her desk, I assume for lunch and she never came back. I was worried the whole afternoon and when came our usual leaving time her bag was still on her desk but I couldn't find her anywhere in the office.

From that day she went into depression that lasted for weeks. After she recovered from depression she has never been the same. No more chats, no more pool, no more shared cooking, no more supermarket, no more waiting for me to leave work. She never mentioned the gift she wanted to give me. When I asked her how come you go to supermarket alone and we don't go together like before she was always very defensive. Left without any explanation I felt hurt and worthless.

Many months later she told me that she didn't know what happened to her. The doctor said she had bipolar but she quickly dismissed and denied that. Also whenever I mentioned that she was not the same as the time we went to beautiful place she always denied. We were still friends after that she has never been the same has before. A lot more distant and passive-aggressive.

So is it possible for someone with bipolar to go from very happy to a sudden depression that last for weeks during the same day? Would that story suggest that my friend suffers from bipolar even though she would never admit?

Thank you!