I think my friend is in trouble?

My friend is an almost 40yo lady, I love her as my friend, we've been friends for about 9 years, we started together at our previous job. She's the only person who I could keep close, during my relationship with my narcissistic ex. Because we worked together I was able to see and speak to her safely.

She's had issues before when we went out and she would drink (too much) .. she was always looking for someone to have sex with. Her boyfriend was sometimes there with her when she was and last time we went out I often got her back to our group because she was out looking for a date.

That has been years though and we haven't been out for at least 5 years.

A few weeks ago she asked me to be her best friend. She was lonely and didn't have any other real friends. For me, like I said, she already was basically my only friend.

But she's acting off.. it's not just expecting more friendly duties or time spending or just calling.. We had a phonecall this week and she used words that she doesn't usually, at times she was overly formal, some times just quite normal, she says she misses me and we were such a good team and she was rambling and I couldn't get a word in and she called me the wrong name.. Not someone elses name but just wrong.

She didn't really sound drunk but she might have been?

She forgot the things I told her when we called as well.. Like she wanted to meet because my kid was with his dad and her kid was going to a friend and we would meet.. and when she asked me the day after she confirmed that we were meeting because her kid wanted another kid to play with.. and I'm like.. oh but I told you my kid's not with me this weekend. Today is the day we were going to meet and we still hadn't confirmed. This morning she told me she couldn't reach anyone so she wasn't sure yet, I told her to let me know if she knows anything. It's almost 8pm and I still haven't heard back from her. I'm happy I did something else with my day - I went for a good long walk so I could bail if she let me know anything -. But I think this is all weird and off and I'm genuinely worried about her.

How do I best approach this?