my mom picks up my friend on time, but my friend's mom is always hours late for me? she's also hours late when we invite her over?

I don't know why our moms do it like this, but:

When my friend wants to come over my mom picks her up.

When I want to go over her house her mom picks me up.

(Our moms are also friends)

My mom tells me something like, tell your friend that I'll be there 4:30. So my mom leaves the house at like 4:15, and picks her up on time.

However, my friend texts me telling me that her mom is gonna be here at 4:30. So I start getting ready at like 4:15. Then it's 4:45, so I text my friend and she tells me her mom needs half an hour. It kinda gets me mad, but I'm like ok at least she'll be here 5:15. Do you know what time she ends up picking me up? 6. Are you kidding me. She does this all the time.

A few times we've invited her and her kids for lunch (her husband and my dad would be at work). She says "I'll be there 3" You know what time she comes? Like 5. Kinda rude.

It's gotten to the point where I'm used to it. My mom's like, set the table, they'll be here in half an hour. "Don't worry, mom, they probably won't be here for another hour" Aaaand I'm always right.

I know you might say that at least she's picking me up, and that I shouldn't be complaining, but my mom always picks up her daughter, too, and she's usually on time, if not 5-10 minutes late.

I really don't know what to do about this, she does this all the time and it angers me.