welcome to the forum.
it is great to see that you are taking care of the religious needs of someone living with you and helping that person to follow the nativity fast.
all orthodox Christians fast ( / should fast; delete as appropriate!) in the days before Christmas; the days before easter (lent) and a few other days. this is in order to resist our bodily desires (gluttony, lust etc.) when we pray as well as fast, it helps us to resist the temptation to sin.
this is a good source:http://www.coptichymns.net/module-library-viewpub-tid-1-pid-494.html
i need to add a few points of explanation.
1. all fasting should be under the guidance of each person's priest.
for example if someone is ill or frail, the fasting rules are usually relaxed.
2. most people aim to (that is; most do not actually achieve) fast completely (no food or water) from the time of waking in the morning to 12 noon for fasts where fish is allowed (eg. most of Christmas / nativity fast) or till 3pm (eg. wednesdays and fridays and the lent fast).
a few people (monks, nuns, priests and a few other people) abstain from food and drink till even later in the day.
if the person you are looking after is in a residential home because he/she is old or frail, they would not normally be expected to do this. some old people fast till 9 or 10 am, or whatever they can manage. this is under the supervision of their spiritual father (priest) who takes into consideration any medical conditions when advising on fasting.
3. all the days from 25th november to 6th jan inclusive are fasting days which are basically vegan (no mammal meat or dairy or eggs) but fish, including shellfish is allowed most days.
the exceptions are wednesdays and fridays, where only vegan food is allowed.
4. there is an extra fasting day on 19th jan (vegan food) as it is the day before the feast of epiphany. epiphany is usually on 19th jan, but the church year is moving forward a year for those on the old calendar, because the calendar is falling out of synch with the common calendar.
5. some orthodox Christians are on the new calendar (together with most catholics and protestants) which is the same as the common calendar in general use.
others (copts, russian orthodox, armenians, ethiopians etc.) are on the old calendar. it is something to do with the byzantine empire and really quite complicated!
6. Christmas for coptic Christians falls on the night on the 6th January (after midnight, so it's technically on 7th). we fast with vegan food all day, and abstain from food for several hours in the morning. then all but the strongest eat a mid day meal and finish the eating and drinking (i don't mean alcohol! we don't drink during fasts and hardly drink the rest of the year) by 3pm. this is so we can fast the required 9 hours before Holy Communion.
we put on our best clothes and go to church around 6 or 7 pm (all timings are approximate for most orthodox cultures - there is a big difference from northern europe style cultures like north america and australia).
there are lots of special prayers and singing, and then we move straight on the the Christmas liturgy. it is very exciting, and the best bit is when we take Holy Communion at midnight. there is then an (optional) party in the church or in people's houses where we chat and enjoy the foods we have abstained from. we sleep very late, then get up late on 7th and spend the day visiting or 'phoning family and friends.
Christmas is the second most exciting day of the year after easter (Pascha). when we break our fast, we do this for an important reason. although fasting and prayer help us to get closer to God, if we were always fasting we would rely on the outward bodily fasting and not concentrate on allowing God to renew our lives inwardly. we would (probably) also become self-righteous and proud of all our fasting. so the church wisely lets us break our fast, so we can work on praying and studying the Bible without fasting. this way the fasting is a tool to help us in our spiritual life; not the ultimate aim.
i hope others can help plug any gaps i may have left!
also please feel free to send me a personal message if you or your coptic friend have any questions