Alex, from Notts Ladies, pipped fellow girl international Heidi Baek by one shot in the open event at Heswall. Both 14 year-olds helped England win the Girls Home Internationals earlier this month.
During the 72-hole event Alex equalled the course record she set last year with a three-under 71 in the second round.
Meanwhile, Elizabeth Mallett of Sutton Coldfield Ladies shared second place in the girls U14 event.
The championship was preceded by the annual U16 mixed match between England and Spain. The honours went to Spain this year, winning 8½-3½.
Wiltshires Hannah Turland (Tidworth Garrison) was unbeaten in the match, pairing up with Elizabeth Mallett to halve her foursomes and winning her singles 5/4. England was also represented by Hayley Davis (Ferndown) and Sophie Godley (Lindrick).
CSS 74 all rounds
Girls U16 championship
295 Alex Peters (Notts Ladies) 74 71 76 74
296 Heidi Baek (Felixstowe Ferry) 72 78 73 73
306 Helen Searle (West End) 79 76 78 73
Girls U14 championship
303 Mar Giminez Roig (Spain) 73 81 72 77
308 Natalia Escuriola Martinez (Spain) 75 79 74 80; Elizabeth Mallett (Sutton Coldfield Ladies) 73 77 78 80
Full details: www.heswallgolfclub.com.