Could an Israeli court hearing a plea for custody and relocation by a parent returned to Israel with a child in a Hague Convention case abroad, be antagonistic because of the 'history', so that chances of success are slim?

No, there have been a number of cases in Israel in the last few years where mothers of young children who have been returned under the Convention, have fought custody and relocation cases to European countries, and won them, after having earlier returned to Israel following Hague Cases. They will get a fair hearing, and the child's best interests, as perceived by the court, will be the overriding factor deciding the case. A court may be sceptical about the parent's good faith – regarding honouring future visitation if allowed to leave Israel with the child, especially in the absence of substantial financial guarantees. Where real bias against a party is suspected, the option of asking for the judge to disqualify him/herself is always open.