my first reaction is "NOOOOO!!!!" but I don't know what kind of expierance you have had and how the horse is... however I would take into account a few things that are sometimes not the best together:
3 years old
Now, I am not saying any of these things are bad... I have nothing against 3yos (I work with a lot!) or mares, but they WILL get moody sooner or later and that can be a real pain depending on the horse, or arabs, they generally have good feet and are smooth and well built, however they can be high strung. This also can make it hard to keep weight on. All of these possiabilities combined initiated my initial reaction... its just something to take into account.
I would highly suggest having a trainer help you. I would say 9 out of 10 people I have met/talked to/worked with that bought their first horse without a trainer were not happy with how it ended up or wished they had known "what they knew now- then" inclucing myself. You can't judge a book by its color, I looked at many "beautiful" horses but when I saw the horse it was not close to what I needed... then I saw a sun bleeched, dry, dull, scraggly haired, skinny horse in a field in the summer.... forgetting first impressions I got on and rode him and saw him again etc.... I ended up buying him and he was most certinly one of the best horses I have ever worked with. He was a diamond, he was just so caked in dirt no one would have ever known- turned out he was actually a beautiful black horse that looked like a dunishbay and he put weight on and got all shiny etc. just goes to show don't judge a book by its cover. A horse can look great on paper but in reality they can be a nightmare.
Having said all of this- a lot depends on what you actually want to do with the horse... some things I said may not apply in the slightest to you depending on what you want to do with your horse.
In short- I would highly suggest a good trainer that knows you and a friend or 2 oor a family member also try and look at the horse like you don't love it- like the mindset of "even if this horse were perfect im not sure ill buy it" to stay more OBJECTIVE to make sure you get the RIGHT horse that will be a good match vs falling in love at first sight and letting your emotions overtake your judgement and decision making.
Let me know if you have any questions- hope it helped!
Congrats and good luck!