As a rule of thumb, Artscroll translates and elucidates according to Rashi’s commentary. As the editors write in the introduction (to the English edition, but the same appears in the Hebrew edition) “[t]he translation and commentary almost always follow Rashi, although other opinions may be mentioned in the notes”. But what they fail to mention is that when Rashi’s commentary is not “frum” enough, it gives them good reason to deviate from Rashi.
In tractate Niddah (2a) the Mishna speaks about how using a Bedikah cloth before and after intercourse is enough to determine here status as tahor. Rashi, in his explaining the Mishnah, writes as follows:
אם ראתה דם אחר כך בבדיקת ערבית והיא שמשה בצהרים לא מטמאינן טהרות דמבדיקת שחרית עד תשמיש, שהרי קודם תשמיש בדקה, ומצאתה טהורה.
If she saw [blood]… when she checks herself at night, and she had intercourse in the afternoon, we do not consider her as Tameh from the morning till the intercourse, since she checked herself before she had intercourse and she found that she was clean.
The problem is that having intercourse in the afternoon is not frum. Well, actually, it depends. In BT Niddah 17a it says:
אמר רב חסדא: אסור לו לאדם שישמש מטתו ביום, שנאמר +ויקרא י"ט+ ואהבת לרעך כמוך. מאי משמע? אמר אביי: שמא יראה בה דבר מגונה ותתגנה עליו. אמר רב הונא: ישראל קדושים הם ואין משמשין מטותיהן ביום אמר רבא: ואם היה בית אפל - מותר
Said R. Hisdah: it’s forbidden to have intercourse in daytime, because it says “you shall love your friend as thyself”. But what is the proof from this verse? Abaye replied: He might observe something repulsive in her and she would thereby become loathsome to him. R. Huna said, Israel are holy and do not perform intercourse in daytime. Raba said, but in a dark house it is permitted.
So while intercourse should be done at night, if the room is dark it can be done at daytime. But, in our day and age it’s not frum enough.
In the English edition, Artscroll avoids the problem by simply not giving a time frame for that example and they just write that the bedikah before intercourse (no word on when the intercourse takes place) is considered a good enough bedikah. In the Hebrew edition, which is much better than its English counterpart in terms of explaining the Gemara, they explain in more depth. So instead of just giving the same example Rashi gave, they write as follows:
והמשמשת בעדים ... הרי זו כפקידה ... וממעטת על יד מעת לעת, כגון אם שימשה באמצע הלילה ונמצאה טהורה בבדיקתה אז, וראתה דם בשחרית, שאינה מטמאה למפרע מעת לעת משחרית של אתמול, אלא מאמצע הלילה בלבד, שהרי נמצאה טהורה אז בבדיקה של תשמיש.It doesn't really change anything in the simple understanding of the Mishnah. But it does show that Artscroll was uncomfortable to give the same example as Rashi, and changed to come of more frum.
And one who checks herself at the time of intercourse, it is considered a valid bedikah, for example, if she had intercourse in middle of the night and she found herself clean, and she saw blood in the morning, she isn't tameh only from in middle of the night onward, since she found herself to be clean in the intercourse bedikah.