My girlfriend (27f) is expecting me (29m) to cancel plans for my friend to come over

My best friend lives in a town near me and we haven’t seen each other in a while. He got made redundant in January so money was an issue for him. My girlfriend suggested inviting him to ours for the night then me and him could catch up over some drinks in the apartment, playing my video games and ordering some food. 

She said she’d stay at her mums to give us chance to catch up in private. This was ant the end of january and I suggested it to him but we haven’t had a chance to make the plans until this weekend.  He’s supposed to be coming over tonight. My girlfriend mentioned that she doesn’t really want to stay at her mums on Saturday so asked me to cancel.

  I told her no and pointed out it was her idea. I said she’s obviously free to stay but he’ll still be coming over and we’ll still be doing everything we’ve planned so she’d have to just sit in the bedroom, maybe play n the Nintendo switch and just read etc. 

She said no and said it’s not fair but I just reminded her the plans have been made weeks in advance and I’m not going to cancel last minute because she doesn’t feel like staying at her mums. 

She said I wasn’t being fair and I should be cancelling if she wants to stay in the apartment. 

Does anyone have any advice on how best to approach this or have any other views on it?

tl;dr my girlfriend suggested igviting my friend over do the evening to catch up and said she’d go to her mums. He’s coming on Saturday and now she’s saying she’d doesn’t want to stay at her mums and said I should be cancelling plans with my friends.