Do not use the citronella collars Also at last they are being banned in England hopefully going through parliament next week.
I agree if new behaviour to see the vet for a check.
The problem with barking is that it is great fun. Dogs realise loads of endorphins when they bark and it makes them feel good so stopping barking is hard BUT not impossible 
If I were to come to you for a behavioural consult I would aks loads of questions re livestyle daily routine exercise chill time etc as sometimes it is the whole habitat rather than one singe thing that encourages the barking.
However in the short term I would look at increasing calm exercise, lots of sniffing on the walks.
I would create a food trail for feeding, so if you feed kibble drop it in a long line in the garden for her to sniff and find(It is knackering and also realises similar endorphins to the barking)
I would increase if possible activites like grooming, if she likes it, gentle activities that will calm her down generally but also keep her occupied.
This on it own will not stop the barking but will hopefully help to keep her busy, give her the endorphin buzz without barking.
Now barking is not her only way of feeling good.
When she does bark I would say nothing ( It is sooooo hard not to bellow at her to tell her to be quiet!) but drop a treat near her. You are NOT rewarding the barking you are giving her an alternative behaviour which is to sniff on the ground. Do this if possible every time she barks (not in the night obviously) and very quickly she will pause before she barks as she is looking for the treat.
If this does not work eg she carries on barking and does not go for the treat let me know and we can do Plan b!
Good Luck!