Welcome!
Good for you in recognizing that you have needs too. Not only that, you are as important as your daughter. Some suggested reading is "boundaries" under the drop down menu "tools" up above on this page.
Have patience because establishing boundaries is trial and error, may need to be modified as you go along. The boundaries have to have a consequence you can enforce. What are you willing to do( for example, suggesting another day for her visit,( only if you want) because you are not available on that day. Or you can tell her while she can't visit for the day because you are unavailable, you can talk to her on phone for a set amount of time( 15 mins, 1 hour , whatever) and let her know you have a hard stop at that time. Also keep in mind with BPD , the situation with her( GF argument) will fluctuate many different times but you can choose not to fluctuate with her mentally. The self harm threats are scary , we know. Here is some suggested reading on that :
https://bpdfamily.com/message_board/index.php?topic=199594.msg12243007One way to deal is to let her know you will call 911
Please write back to us as you are able.