Sadly I think skidoodly makes a valid point and your partner's interests would be best served if you stood back a bit and keep emotions separate from practicalities.
"In the process of developing a position during a conflictual divorce, a spouse typically is surrounded by an increasing cadre of supporters. These are friends, relatives, and professionals who, after hearing only one side of the dispute in vivid, distorted, and compelling detail, rally to that spouse's side. Viewing that spouse as victimized by the other spouse, they seek to right a wrong and protect the spouse from being further victimized. Johnston and Campbell (p. 25) elaborate on this dynamic:
?The total effect is that, in the absence of socially-agreed-upon customs and etiquette for organizing postdivorce relationships and dealing with conflicts of interest, there is considerable ambiguity. Consequently, the social networks of the spouses are incorporated into the dispute and the dispute is solidified, maintained, and stabilized by the support of others. New partners, extended family and kin, mental health professionals, and lawyers fuel the fights and in some instances take on the dispute as their own. As the conflict escalates and spreads, the primary players may not be the two divorcing partners but all these others who are not party to the stipulations, court order, or legal sanctions."
This support by the associates of each of the spouses takes on the complexion of tribal warfare, with parallels to the ways that we stereotypically imagine primitive villagers dealing with their conflicts. The sides are drawn, the supporters are garnered, and war is declared. Unfortunately, the toll taken on the children in this insidiously dysfunctional social process is legend (Wallerstein & Kelly, 1980; Wallerstein & Blakeslee, 1989). Researchers and clinicians for years have interviewed and counseled countless adults who recall vivid childhood memories of their parents' conflictual divorce experience as a living hell of divided loyalties, forced court-ordered examinations, pressure to take sides, and the absence of any sense of security, safety, trust, or sanity." - Child Clinical Psychologist, Donald T. Saposnek, Ph.D. & Chip Rose, JD, CFLS
Family law is very specialised. As I said above the court has no jurisdiction to make a contested order for child maintenance or a variation. See s8 Child Support Act 1991 as amended. The exceptions are;
a)cases predating March 2003,
b)a child of the family is a step child,
c)one parent lives abroad,
d)over 18s in education or training,
Unless your partner has an order predating March 2003 it appears the only option is to apply for a s8 order to regulate parental responsibility under the Children Act 1989. However, there is a no order principle where courts are directed only to make an order if it is necessary and makes things better for a child. The paramount concern is the best interests of the child, not parental rights or fairness.