My cat is acting wacky

I don't know exactly what causes it but sometimes as a cat gets older their personality just changes. My girlfriend's family has a cat who's probably 13 or 14 now and up until a few years ago she was a very solitary cat and wanted to be left alone.

Now she wants attention all the time! So in this case it was a good change, she's a good cat

Have you taken her to the vet to rule out any medical problems?

It has been only recently she has started wandering out? How long have you had her? Has she always been indoor/outdoor?
First and most important is to have a thorough vet exam. Is she up to date with vaccines and treated regularly for parasites (worms, mites, ticks, fleas....)?
If your kitty is given free rule of indoor and outdoor, there could be so many different reasons for a sudden behavioral change. Is it that difficult to keep her indoors over the winter season?

I used to take Lucky and Bugsy to the garden with me, supervised, until that they started whining too much to go out... all the time.
They would go to the door and scratch it scratch it and scratch it... It was gradual, but it got to a point that I was getting tired of the whining, so I decided that to make them happier, along with some other reasons, like - sparing them from flea meds, and mosquito bites the best thing to do was to not let them outside anymore - ever, period.
At least until I have my own house and can have their enclosure... until then... nope.
In the beginning they continued to whine... all the time... and run to the door... and all that...
But with time that behavior surely faded away, and they are completely content in being inside. No more whining, scratching on the door...
Bugsy still comes when I open the door, but doesn't attempt to run.
Lucky did run once - she went three feet away ...
It took patience, but surely it worked - now they are perfectly happy watching the outside from the window.
IMO as long as you let her go outside, she will always whine to go out.
If you want to cut that behavior you need to keep her in 100%, and make her time inside interesting.
Maybe a playmate? Shelves, and windowsill always helps, cat trees... lots of vertical space....
It will be annoying in the beginning, but she will get over it.
It is way too cold to be outside.... This week here is Dallas with the wind feel We got 6-7F during the night... That is absurdly cold. During the days most of this week we were under freezing temps... Right now it is 18F... She is not safe outside, and at these temps, water is not water, it is ice...

I agree with Carolina Just bring her in and keep her in. There are too many dangers outside. It will be an adjustment since she's gotten used to it but I feel it will be safer for her in the long run.