flaky friend

i (21 f) have had a good friend (21 f) for about 4 years now. we met in school and have been friends since. she has always been relatively flaky on plans but the past year or so it has gotten worse. i try to make plans with her all the time and she agrees to them and then either cancels last minute or just does not reply. she lives 2 minutes down the road from me and i have seen her about two times this year. i try to give her grace because her brother passed away unexpectedly about 2 years ago and i cannot imagine the toll that has taken on her so i really try to be empathetic of that but it’s starting to become too much. we made plans about 5 days ago to go out tonight and i have been texting her about it since then and she has fully agreed to a time and place. she texted me this morning basically saying she knows she’s going to flop so she just wants me to let me know now. its been a running joke that if i have plans with her i really don’t but it’s honestly not funny anymore and it’s getting old. i told her that exactly and i explained how her doing that not only hurts my feelings and gets my hopes up but also effects my plans and my whole day. she basically said she knows and she feels bad but she is depressed and doesn’t want to do anything but she feels like if she says no to me initially i will be mad and if she says yes then flops then i will also be mad. which yes it would be upset but im mainly upset because i want to see my friend. i completely understand being depressed and having little motivation to go out and socialize but it’s been like this for over a year and i don’t know what to do anymore. i want to support her and be there for her but i don’t know how to. and it also gets to a point of are we even still friends if i see her a few times a year? and we both only work part time so our schedules really aren’t even an issue. i’ve offered different things to do and things that don’t require lots of interactions. i’ve even offered to just sit with her in her room. but i can never seem to have a set plan with her that sticks. i’m just not sure what to do at this point. she’s said to me many times that i am her only friend and the only person she has and i feel terrible about that. i want to see her and hang out with her but i am not someone that can maintain a solid friendship only seeing each other a few times a year and talking here and there. especially when we live down the street from each other. i don’t need to see her everyday but like i said ive seen her twice this year and once was because she was working the venue of my graduation. i love her to death but it’s becoming exhausting to continue what feels like carrying our entire friendship on my shoulders. any advice is appreciated, thanks in advance and i apologize for this being kind of all over the place.