Hen refusing to go to bed!

Hi. I'm a little worried about one of my 4 hens, Agnes. she's suddenly refusing to join her sisters in the coop at night. She's taken to roosting on the outside perch and when i go to shut them up i have to pick her up and put her in the coop with the others.
 I don't know if this has anything to do with it but over the last 2 weeks I've found 2 soft shell eggs and one egg with no shell. this last one was in the nesting box with 4 others, which means 5 eggs from 4 chickens! but since this i've only been getting 3 eggs a day. I can't be sure it's Aggie but she doen't seem her usual self .  What should i do? Thank you.

There's no sign of redmite. I clean the coop every day and dust every 6 weeks.
I left shutting them up tonight until it was dark thinking she might go in later if given time. but she had gone to roost on the outside perch.
the other 3 gal's were all quite happy in the coop.
do you think if laying the strange eggs caused her pain that could be why she wont go to bed?
If i take the outside perch away do you think that might help?
I'm realy worried about her

Thank you. She layed another soft shell today, all strunched up. she also had egg round her beak so i guess she ate the contents. i can see her sitting on the outside perch now so i'm going to put her in

Good news, Agnes went to bed last night she also laid a normal egg this morning, although it still feels lighter than the others and is white. Do you think worming them helped? can only one chicken be effected? i will now worm them every 3 months!!