As per my experience as a Marriage Counsellor, certain people don’t like the intervention of the 3rd person at all. Some think we all know what to do. Some due to ego won’t turn up for marriage counselling. Some may avoid visiting a marriage counsellor as they knew the suppressed issues will come up on the surface. So to convince your partner for marriage counselling:
First, Convey and accept in front of your partner that you are also wrong on certain aspects. We can clap only with two hands so more or less both people are responsible for the situation.
Second, tell her that professional marriage counsellor may be able to make us aware of our flaws and the chances are higher to work on them as they have certain skills to do so.
Third, Numerous times one person shows inhibition or resistance and later gets agreed for the same n found counselling beneficial for a longer run. If possible, visit a marriage counsellor individually first and explain your situation. Please understand, you can’t change your partner, you can change yourself. Once you change yourself, your partner will automatically change.