> my question is should i feed her twice a day, measure the dry food recommended allowance on the bag and feed her twice,
I like twice a day - it suits my two, but I can see how one meal might suit you best. Your girl may well be horrified though and that makes it harder for you.
With regard to portion management I don't feed what's on the bag. Sometimes those allowances are too high (or too low!). Whatever you have her on at the moment I'd recommend weighing it for accuracy - when you guestimate you can easily be adrift by up to 20g per meal and that can make a huge difference to your dogs end weight. In order to manage the 'extra few biscuits' challenge just weigh her daily portions in advance. I still weigh mine each day and use the chinese takeaway boxes to store their meals in. Saves me faffing about in the morning when I'm trying to do other jobs as well.
If you weigh in advance you can take everything from that allowance - her 2 meals per day, a few extra's whilst she's walking with you, some to sling in an activity feeder - whatever takes your fancy (and hers). If you have some left over at the end of the day she can have supper too!!
One thing to remember about poo if that if you feed too much, you get large quantities of 'wet' output. That might indicate you have an issue with her portions rather than the quality of food you are feeding? It also obviously depends on body type, exercise, size, age etc. I feed Arden Grange and have a 6yo of 13kg on 150g per day and a 20 month 27kg dog on 480g per day - I don't think either of them correlate to the recommended feeding amounts! I can shift or add weight to my youngest if I change only 5g per meal for a week. Good luck