HELP, dog with 1 floppy ear?

Our gorgeous girl Cassie is a border collie x kelpie she is about 4yrs old (roughly my mummy memory is shocking) and this morning i have noticed that 1 of her ears is flopping forward.
Normally when you call her both ears perk up and she comes running.

I noticed it so called her in and it didn't move, she let me touch it, i held it up and it flopped straight down again, she kind of looks like a rabbit :p

Is this normal, does it mean something is wrong?

We have just moved and although she used to being out at night on the property we have been keeping both our dogs (jack 3yrs old) in the yard but they have been getting out.
Cassie seems to 'go missing' during the day and quite often takes a while to call back.

I hope nothing is wrong with her... please please help!

Is the floppy ear inflamed at all? Thick? Often when they get ear infections, or even aural haematomas (I'll explain in a sec) they let their ears flop as its painful. It could be that? Its hard to know without having a look at the ear and inside it.

Aural haematomas happen when they shake their heads due to fleas or ear irritations like flies... and they burst a blood vessel in their ears and it fills up slowly with blood. Often if they are bad, vets will put a drain in to let the blood drain out slowly, or they just pull it out with a syringe and see if it fills up again before going through anaesthesia. Most of the time pulling the blood out with a syringe & needle doesn't work, but its good to know there are options.

Will have to have a look, i didn't really look in the ear as DD1 was trying to push her way out to see the dogs, will check when she goes to bed!

I'd check it out thoroughly but don't panic if you don't find anything wrong, we have a Silky who has a floppy ear, doesn't really ***** up but I think its pretty cute lol

ear leathers can 'break' as such and become floppy
she may have an inner ear irritation but i highly doubt that would make it floppy...if you are at all concerned or she seems in pain/bothers her get her seen by your vet