Hi, Missmouse
My sympathies. My mum (almost 90) has mixed Alz and vascular dementia and has been in residential care for nearly five years now (in a nursing unit since spring 2014). During that time, she has been bed-bound for long periods (about a year to 18 months from mid 2014 to spring this year).
She had become that way gradually, losing her independent mobility (walking very slowly with a stick/handrails), then needing a wheelchair to sit in the lounge during the day, then staying mostly in her room in the wheelchair or armchair, then bed-bound. Once she had reached that stage, it seemed impossible to me that she would ever improve at all, and I developed a routine of spending time with her just at her bedside.
Last Christmas, she suffered an acute health crisis (aspiration pneumonia) and had to be taken to hospital. I thought this was the end (the shock of being moved out of the home in itself would be likely to kill her); but in fact, after treatment with IV antibiotics and a period of further bed-bound fragility in Dec-Jan (where she needed feeding, too weak to feed herself), she rallied and has been able to spend days in the wheelchair in the lounge again - and even sit out in the garden for an hour or so a few times this summer, which she had not previously done since 2013 (her unit is on the first floor and when mobile she could not manage stairs and would not go in the lift; now she tolerates this in the wheelchair).
So I would say just take it slowly; you may feel it's terribly sad for her to be confined to her bed and not socialising as before, but if she is physically too weak even to be moved without a hoist, a shopping trip (with all the stress that entails) is probably too big a leap to aim for. For the moment, I wold suggest finding ways to entertain her quietly in her room - gentle music, non-stressful TV/radio, if she still enjoys that and is able to watch from her bed, perhaps reading to her or just sitting quietly alongside and making a bit of conversation.
I found that when mum was frailest, most things we take for granted to entertain us (narrative TV or noisy entertainment programmes) were too much for her. She just wanted to be quiet and peaceful. So I would concentrate on making the immediate environment as pleasant as possible - fresh flowers, perfume, nice toiletries, etc. Small treats to tempt the appetite - strawberries, slices of banana, cake in digestible portions, drinks in easy to handle cups.
Photos, if she still shows interest in these and they don't disturb her (my mum is sometimes confused or distressed by even precious family photos that she can't now place in context).
And then, if she gains some strength, progress gradually from bed to chair (with help and pressure-relieving cushion if immobile for long periods), ideally so that she can see out and maybe enjoy a view of the garden/birds, window box, plants. Then, if she's strong enough for that, in a wheelchair to other rooms in the house, and garden if accessible.
There's no point trying to engineer a bigger trip straight away, if she's not yet strong enough to enjoy it, as it will be stressful for both of you and may in fact set her back. Little steps. If a standard hoist is too big, investigate whether there's something smaller that you could get into the room to help lift her at least out of bed into an armchair or wheelchair.
Your company and these small comforts may be all she really needs or wants at the moment; and then if she gains strength by keeping up her bodyweight and recovering from any acute illness, she may gradually be able to return to a degree of wider socialisation.
I was very surprised my mum was able to go out in the lounge, let alone garden, this year, having been bed-bound for 18 months before. She is now back to spending most of the day in her room, as too much stimulation is tiring for her (and other residents sometimes annoy her! She likes her privacy); but she is still able to sit in an armchair and feed herself again to an extent (eating mostly with fingers and drinking from light beaker). Just take it slowly and set small goals; take your cue from her own mood.
All the best.