JanHR - been through this with both mine. dd is now 19 months and still wants boobie a lot. I have to say its quite easy when I am typing on mumsnet but I know how you feel. Several questions I would ask you -
How is she eating? Check that she isn't genuinely hungry.
Is she sickening for anything - she may need the extra milk to help stave off an infection. Also babies need extra comfort at teething times.
Is she upset about anything else and needs comforting.
Is she bored?
I find it easier just to give in but make the 'feed' short (sometimes this has to happen anyway because I have to attend to ds) and I just pull her off and by the time I come back she's probably forgotten. She won't pull at me unless I am sitting down so your ds may be genuinely upset (difficult for me to say without seeing her). How long has she been like this - has she suddenly started to 'ask' for more recently. In the long term I'd say try to make a particular chair/place where you breastfeed preferably in her bedroom so she isn't constantly reminded by it. Go to it initially as much as you want and then gradually do distracton techniques and hopefully she should just associate that chair with the breastfeeding.
Over night is harder I know - it doesn't go on for ever - ds stopped feeding in the night around age 2 and we co-slept. Depends what you want to do. However you would be surprised at how well they cope without you being there. Your dh could maybe take her out the car to settle her when you have your night out, or maybe put her to sleep in a pushchair as she may not associate that with mummy. She may respond well to weaning when she is a bit older. my sister's son weaned at 22 months when his dad went to him in the night and he said "no boobie?" or something like that and seemed quite happy to let him settle him.
I started to put dd in her cot at 18 months for daytime naps and she seemed to like the novelty of it with the musical toys etc round her but did cry but only for a minute. I will then move onto the night time. I did this with ds, with daytime naps and then nightime - he'd only sleep part of the night on his own to start with and gradually it extended.
I doubt if your dd will be happy with just expressed milk when you are out as it is likely that it is the comfort she is looking for - she may be fine when you aren't around to 'remind'her of it.
can post more but run out of time just now!