
There is no hard and fast rule that as soon as they reach six months you have to cut out a meal. I usually keep three going until around nine months unless they stop eating one (unlikely in a Lab). If you want to cut it down now then I would gradually cut down the lunchtime one, you can spread the cutting down over whatever period you feel happy with.
Whether you up the others will depend entirely on her weight. If the vet has advised this he may feel she is overweight, if this is the case then leave the others as they are. If she is a correct weight then add a little more or wait until you see if she is losing any.
You can always just pop a few biscuits in her bowl at lunchtime, just so she has something if you feel it is necessary.
Most important is that you are giving her a quality food in her two feeds, if she is on proper food at lunchtime and not at breakfast, then make it two meals of proper food.
Sandra