This weekend DD is off to a Halloween party (16/17 age group). It's been planned for ages, there's been a lot of effort in getting costumes and everyone's very excited.
Today, there's been a last minute addition to the guest list, who we'll call L. L had planned a Halloween party of her own, but all her friends have ditched her to go to another one (which I assume she's not invited to). Feeling sympathetic, her sister's asked if she can come along to this one. The host has agreed, although other people who have asked and would have been welcome have been refused due to numbers.
The problem is that no-one at this party (including DD) likes L, and she doesn't know many of them very well. She's autistic with a strong personality, and has trouble reading people (like when people are joking), let alone when those people are drunk. It's likely some people will be mean to her and she will start arguments by misreading a situation or just not knowing who's currently dating/split up.
DD is one of the people she does know, and says that L always latches on to her, so that she can't socialise and enjoy the party. She is a kind girl, but says that more than 15 minutes with L makes her feel panicked and stressed and she has previously made excuses to miss social events to avoid her.
L isn't confident in social situations and may not go. Obviously, no-one wants to say that they don't want her to come and people feel sorry for her. But at the same time, they are afraid she'll spoil the evening, and won't enjoy herself anyway.
Does anyone have any useful advice on how to tactfully resolve the situation?