Good advice on the spaying C, I aim to let her have at least one season, maybe more. With regards to the harness did you train her to a slip lead separately, and only use that at heel then? I have never used a clicker, but could try that to show approval, but it will therefore have extremely limited utility, I must do some more reading, and rely less on the black magic!
She is always in the harness as when she goes out on a walk she will want to walk forward of me as eager to use her nose and find things to smell. I don't not make her heel I just let her get on with it, she then calms after ten mins or so. At this point she will be either off the lead or walking to heal naturally......I have never used anything other than a harness as if a dog does pull ...well I know I wouldn't want something choking me if I was her...hence the harness does not do that. I have been told in the past use a harness only when working as the dog will know when its time to work....well with Piper I just have to say 'find the deer' and she is knows it means fun and blood to sniff ))
Regards basic training and clicker training there are some excellent trainers on there , all using positive re-enforcement.